The invention relates to novel water ices aerated with a water soluble gas. In particular the invention relates to novel water ices aerated with a water soluble gas which contain an antifreeze protein in their composition.
It is highly desirable to be able to manufacture a water ice having novel shapes, properties and/or textures. Until now, however the ability to provide such a high degree of novelty and interest to the products has been limited. In particular products have to be manufactured with the ability to survive packaging, storage and distribution.
It is especially desirable to be able to provide a water ice that has a low calorific content. Such a water ice has the advantage of being particularly refreshing.
However, if a low calorie containing water ice is manufactured in the conventional way a very hard block of ice is achieved which is not acceptable to the consumer when eaten at typical freezer temperatures.
Products which have been aerated by soluble gases such as carbon dioxide and/or nitrous oxide have been disclosed in the literature. Examples are U.S. Pat. No. 3,969,531 and JP 80013708.
U.S. Pat. No. 3,969,531 (Cornelius) discloses a process whereby a water and orange juice mixture is aerated wish nitrous oxide gas to form a semi frozen comestible.
JP 80013708 discloses a granular frozen drink that may be drunk through a straw. A syrup is mixed with the water and carbon dioxide within a machine for manufacturing a frozen drink such that a carbon dioxide gas is located among the frozen material.
U.S. Pat. No. 4,826,656 describes a smooth textured soft frozen water ice with a solids content of 18-26 wt % and an overrun of between 25-70% using air, where the water ice contains from 0.05 to 0.5 wt % of a stabilising mixture.
GB 915 389 describes a fat-free ice cream containing dispersed air or gas so that it is easily cut or bitten when cold.
However we have found that such products have stability problems such that they cannot be further processed, for example they can be difficult to extrude, and also they are not storage stable at xe2x88x9218xc2x0 C.
In our co-pending application PCT/EP 99/0029 (published as WO 99/38386 on Aug. 5, 1999 after the priority date of the present application) a water ice product which is stable to processing and storage at xe2x88x9218xc2x0 C. is provided having a channelled porous structure. However it is disclosed in WO 99/38386 that stable water ice products aerated with water-soluble gases cannot be provided if the product has a gas phase volume of greater than 0.45 after hardening. We have surprisingly found that water ice products having an antifreeze protein in their composition may be aerated with water-soluble gases such that a much higher gas phase volume may be achieved.
Additionally the inclusion of an antifreeze protein in the water ice composition provides the ice confection with specific defined mechanical properties. Such water ices have novel textures and/or properties and products may be provided having complex, highly defined shapes. The novel features can be retained during packaging, storage and distribution.
Accordingly the invention provides a water ice comprising an antifreeze protein, a stabiliser and not less than 0.1 wt % of a protein based aerating agent obtainable by a process comprising aerating the water ice with an aerating gas which contains at least 50% by volume of a water soluble gas such as carbon dioxide, nitrous oxide and mixtures thereof.
Preferably the aerating gas contains at least about 50% by volume, more preferably at least about 70% by volume of a water soluble gas, most preferably 100% by volume.
By water ice is meant a frozen solution made essentially from sugar, water, fruit acid or other acidifying agent, colour, fruit or fruit flavouring.
The water ice will typically have an ice content of at least 30% by volume when measured at xe2x88x9218xc2x0 C., more preferably at least 40% by volume when measured at xe2x88x9218xc2x0 C., most preferably at least 50% by volume when measured at xe2x88x9218xc2x0 C.
The ice content may be determined following the techniques described in the article by B de Cindio and S Correra in the Journal of Food Engineering, Volume 24, pages 405-415, 1995. The enthalpy data required for this technique is obtained using adiabatic calorimetry (Holometrix Adiabatic Calorimeter). The ice contents as expressed herein are measured on an 80 g sample poured into the sample holder of the calorimeter and cooled to xe2x88x9275xc2x0 C. by placing the assembly in dry ice prior to placing in the calorimeter (precooled to between xe2x88x9270xc2x0 C. and xe2x88x9280xc2x0 C.). The enthalpy data obtained was analysed to give ice content as a function of the temperature following the method of Cindio and Carrera.
In general the water ice has a total soluble solids content of less than 40% by weight, preferably less than 25% by weight, most preferably less than 15% by weight. For low calorie water ices the soluble solids content may be as low as approximately 5% by weight.
Typically the total soluble solids of the composition used to make water ice product of the present invention is in the range 5 wt % to 30 wt %, preferably 6 wt % to 25 wt % for example 7 wt % to 20 wt %.
The total soluble solids content is measured at 4xc2x0 C. and is the % by weight of the total composition that is dissolved at that temperature.
A further advantage of water ice products which have been aerated with a water-soluble gas is that they are surprisingly provided with a surface which is substantially free from stickiness. Usually a non-sticky surface is obtained.
The water ice, must include within its composition a stabiliser and not less than 0.1 wt % of a protein-based aerating agent. Preferably a stabiliser is included in an amount of at least 0.1 wt %. The maximum amount of stabiliser is about 1.0 wt %. Preferably the amount of stabiliser is in the range of from 0.1 to 1.0 wt %, more preferably 0.15 wt % to 0.7 wt %, for example 0.2 to 0.5 wt %. For a given formulation and/or processing conditions the exact amount of stabiliser required will depend on the type of stabiliser used. The amount of stabiliser refers to the total amount of stabiliser(s) in the product.
As used herein the term xe2x80x9cstabiliserxe2x80x9d refers to compounds conventionally referred to in the art as stabilisers. They improve the stability of the water ice composition before freezing and act as thickening agents. It is believed that they increase the viscosity of the liquid phase before and during freezing.
Any stabiliser may be used, however Locust Bean Gum (LBG) is the preferred stabiliser. Other stabilisers that may be used include Agar-Agar, Algin-sodium alginate, proplyene glycol alginate, Gum acacia, Guar seed gum, gum karaya, oat gum, gum tragacanth, carrageenan and salts thereof, furcellaran and salts thereof, psyllium seed husk and cellulose stabilisers. Mixtures of any of these stabilisers may be used.
The amount of protein based aerating agent in a product aerated with water soluble gas is not less than 0.1 wt %. The typical wt % range for the aerating agent in the composition is 0.1 wt % to 0.5 wt %, more preferably 0.15 wt % to 0.4 wt %, more preferably 0.15 wt to 0.25 wt %.
An aerating agent, as the term is used herein, refers to any component which because of its surface activity and/or the viscosity it imparts, aids the formation of smaller gas cells (than would otherwise be formed) and resists their coalescence or separation in the unfrozen matrix.
Any protein based aerated agent may be used, for example egg based aerating agents such as egg white, sodium caseinate, soya isolate, wheat gluten and whey protein. Preferably the aerating agent is a hydrolysed milk protein such as Hyfoama (Trademark from Quest) and hydrolysed soya protein such as D-100 (trademark from Gunter Industries). The aerating agent is to be understood not to include aerating gas as referred to below.
By antifreeze protein (AEP) is meant a protein which has significant ice recrystallisation inhibition properties as measured in accordance with Example 2. The AFP provides an ice particle size upon recrystallisation of less than 20 xcexcm, more preferred from 5 to 15 xcexcm.
Preferably the water ice comprises at least 0.0005% by weight antifreeze protein, more preferably 0.0025% by weight antifreeze protein. Typically the water ice will comprise from 0.0005% by weight to 0.005% by weight antifreeze protein.
For some applications it may be advantageous to include a mixture of two or more different AFPs into the water ice.
The AFP for use in products of the invention can be any AFP suitable for use in food products. Examples of suitable sources of AFP are for example given in the article xe2x80x9cAntifreeze proteins and their potential use in frozen food productsxe2x80x9d, Marylin Griffith and K. Vanya Ewart, Biotechnology Advances, vol 13, pp375-402, 1995 and in patent applications WO 98/04699, WO 98/04146, WO 98/04147, WO 98/04148 and WO 98/22591.
The AEPs can be obtained from their sources by any suitable process, for example the isolation processes as described in the above mentioned documents.
One possible source of AEP materials is fish. Examples of fish AFP materials are antifreeze glycoproteins (AFGP) (for example obtainable from Atlantic cod, Greenland cod and Tomcod), Type I AFP (for example obtainable from Winter flounder, Yellowtail flounder, Shorthorn sculpin and Grubby sculpin), Type II AFP (for example obtainable from Sea raven, Smelt and Atlantic herring) and Type III AFP (for example obtainable from Ocean Pout, Atlantic wolffish, Radiated shanny, Rock gunnel and Laval""s eelpout). A preferred example of the latter type is described in WO 97/02343.
Another possible source of AFP material are invertebrates. Also AFPs may be obtained from Bacteria.
A third possible source of AFP material are plants. Examples of plants containing AFPs are garlic-mustard, blue wood aster, spring oat, winter cress, winter canola, Brussels sprout, carrot, Dutchman""s breeches, spurge, daylily, winter barley, Virginia waterleaf, narrow-leaved plantain, plantain, speargrass, Kentucky bluegrass, Eastern cottonwood, white oak, winter rye, bittersweet nightshade, potato, chickweed, dandelion, spring and winter wheat, triticale, periwinkle, violet and grass.
Both natural occurring species may be used or species which have been obtained through genetic modification. For example micro-organisms or plants may be genetically modified to express AFPs and the AFPs may then be used in accordance to the present invention.
Genetic manipulation techniques may be used to produce AFPs. Genetic manipulation techniques may be used to produce AFPs having at least 80%, more preferred more than 95%, most preferred 100% homology to the APPs directly obtained from the natural sources. For the purpose of the invention these AFPs possessing this high level of homology are also embraced within the term xe2x80x9cAFPsxe2x80x9d.
The genetic manipulation techniques may be used as follows: An appropriate host cell or organism would be transformed by a gene construct that contains the desired polypeptide. The nucleotide sequence coding for the polypeptide can be inserted into a suitable expression vector encoding the necessary elements for transcription and translation and in such a manner that they will be expressed under appropriate conditions (for example in proper orientation and correct reading frame and with appropriate targeting and expression sequences). The methods required to construct these expression vectors are well known to those skilled in the art.
A number of expression systems may be utilised to express the polypeptide coding sequence. These include, but are not limited to, bacteria, yeast insect cell systems, plant cell culture systems and plants all transformed with the appropriate expression vectors.
A wide variety of plants and plant cell systems can be transformed with the nucleic acid constructs of the desired polypeptides. Preferred embodiments would include, but are not limited to, maize, tomato, tobacco, carrots, strawberries, rape seed and sugar beet.
For some natural sources the AFPs may consist of a mixture of two or more different AFPs.
Preferably the antifreeze protein is chosen such that it gives an aspect ratio of more than 1.9 to the ice crystal, preferably from 1.9 to 3.0, more preferably from 2.0 to 2.9, even more preferred from 2.1 and 2.8 (see WO 98/04146). Aspect ratio is defined as the maximum diameter of a particle divided by its minimum diameter. The aspect ratio can be determined by any suitable method. A preferred method is illustrated in the Examples (Example 3).
For the purpose of the invention the preferred AFPs are derived from fish. Especially preferred is the use of fish proteins of the type III, most preferred HPLC 12 as described in our case WO 97/02343.
Surprisingly aerated water ice compositions containing antifreeze proteins have similar mechanical properties if they are aerated with air or with a water soluble gas.
Accordingly water ice compositions containing antifreeze proteins which have been aerated with a water soluble gas have the following mechanical properties;
xcex94 modulus/original modulusxe2x89xa70.4, and/or
xcex94 strength/original strengthxe2x89xa70.7, providing that when
xcex94 modulus/original modulusxe2x89xa66.0, xcex94 modulusxe2x89xa790 MPa, and/or
when xcex94 strength/original strengthxe2x89xa62.0,
xcex94 strengthxe2x89xa70.2 MPa.
Most preferably xcex94 modulus/original modulusxe2x89xa71.0; providing that when xcex94 modulus/original modulusxe2x89xa66.0, xcex94 modulusxe2x89xa7100 MPa.
Preferably xcex94 strength/original strengthxe2x89xa70.9. Most preferably xcex94 strength/original strengthxe2x89xa71.5.
By modulus is meant the apparent elastic modulus (E) as determined using a four point bend test. Example 1 gives the standard procedure for performing a four point bend test.
Therefore xcex94 modulus (xcex94E) means the change in modulus between two water ices whose formulation and process of manufacture are identical in all respects except that the first water ice includes in its composition an antifreeze protein, and the second water ice has no antifreeze protein included in its composition (the control composition). Original modulus (Eorig) is the modulus measured in the control composition.
By strength is meant the flexure strength ("sgr"u) which can be defined as the maximum stress that a material can withstand, under the particular conditions. The flexure strength is given by the stress at a point of maximum force on the force versus displacement curve recorded during a four point bend test.
Therefore xcex94 strength (xcex94"sgr"u) means the change in strength between two water ices whose formulation and process of manufacture are identical in all respects except that the first water ice includes in its composition an antifreeze protein, and the second water ice has no antifreeze protein included in its composition (the control composition).
Original strength ("sgr"u orig) is the modulus measured in the control composition.
Products according to the invention have a channelled porous structure.
By channelled porous structure is meant a structure containing voids in the form of tortuous, non-spherical channels. The channels being formed by the gas phase. These structures can be distinguished from known aerated structures where the gas phase forms voids in the form of bubbles, the majority of which are substantially spherical in shape for a gas phase volume of between 0.1 and 0.45.
The structures of products according to the invention can be distinguished from AFP containing structures aerated with a non-soluble gas such as air by the relative diameter of the individual gas channels present in products aerated with a soluble gas being greater for the same overrun than the voids present in products aerated with a non-soluble gas.
Furthermore, the structures can be distinguished from non-AFP containing structures aerated with a soluble gas. In products according to the invention the non-gaseous phase comprises a close-packed continuous network of ice crystals.
By close-packed continuous network of ice crystals is meant that any given ice crystal is connected to at least one other ice crystal.
As mentioned above, the addition of an antifreeze protein into the water ice composition provides the water ice product which has been aerated with a water soluble gas with novel textures and properties.
The water ice containing the antifreeze protein may constitute the entire product or may be a component of a composite product. For a composite product the water ice of the invention is included within a conventional ice confection to provide texture contrast. Preferably such composite products contain the water ice in accordance with the invention as discrete elements in their structure. For example, a relatively soft ice cream core can be coated with a layer of the composition of the invention to provide a hard, crispy layer surrounding the ice cream core. Another example would be the incorporation of the water ice of the invention as inclusions in ice confections. Alternatively the product may be provided with a continuous or partial coating of, for example, a water glaze or a non-aerated water ice on at least one surface.
Water ice products according to the invention, which are aerated with a water-soluble gas, may conveniently be prepared by a method comprising the following process steps;
(i) aeration of a water ice composition with an aerating gas which contains at least about 50% by volume, preferably at least about 70% by volume, most preferably 100% by volume, of a water soluble gas.
(ii) freezing in a freezer, for example, an ice cream freezer, such that the residence time in the freezer is approximately 2.5 to 10 minutes, preferably 3 to 9 minutes, for example 3 to 8 minutes; and
(iii) two-stage hardening.
A water-soluble aerating gas is one with a solubility in water of at least 2 grams/100 g of water at 4xc2x0 C. and 760 mmHg.
The water-soluble gas may typically be carbon dioxide, nitrous oxide and mixtures thereof. The remainder of the aerating gas will typically be nitrogen containing gas e.g. air.
Preferably the aerating gas is carbon dioxide or a mixture of gases containing carbon dioxide.
Aeration may occur within the (ice cream) freezer or alternatively before freezing, e.g., within a pre-aerator before the water ice composition enters the (ice cream) freezer.
Typically the ice cream freezer will be a scraped surface heat exchanger.
It is to be understood that the aerating gas used according to the invention is not to be essentially air, but must comprise a water soluble gas as defined above.
It is particularly preferred that the two stage hardening step mentioned in the process above is conducted as follows:
The two stage hardening step may be achieved by rapid freezing in the first stage to partially form the structure of the ice product, with the temperature of the second stage being suitable for expansion of the structure. The first stage hardening is preferably carried out using a colder temperature than the second stage. The first stage may use air at xe2x88x9220xc2x0 C. or below blown over the product. The hardening step could occur in a single freezer or in a first colder freezer with the second stage occurring in another freezer during storage.
A preferred two stage hardening step is;
(1) The temperature of the product needs to be reduced to below at least xe2x88x9220xc2x0 C. within approximately 2 hours, for example within, a blast freezer, hardening tunnel, liquid nitrogen or any other suitable rapid cooling means. Typically the product is placed in a blast freezer for 1 hour at xe2x88x9235xc2x0 C.; and
(2) The product is then retained at a temperature of approximately xe2x88x9218xc2x0 C. or below until the product density stabilises. This may be effected by storing the product for 3 days in a cold store at xe2x88x9224xc2x0 C. The structure is stabilised when there is no further change in its density.